Recent research conducted on the long-term issue of age distribution of red snapper
in the Gulf of Mexico indicates that older fish, age eight and up are more reproductive
than younger fish were over the previous ten years. The research was conducted by
James H. Cowan, professor, of LSU’s College of the Coast & Environment, Department
of Oceanography and Coastal Sciences, and current and former graduate students Dannielle
Kulaw and Melissa Woods Jackson.

In studies done a decade apart, evidence shows a recent shift toward a slower progression
to sexual maturity as well as reduced egg production, especially among young, small
female red snapper, in the Gulf of Mexico. Slower maturation rates among young fish
ages two to six, lower gonadosomatic index, or GSI, values – - a tool for measuring
the sexual maturity of animals — and decreased spawning frequency were observed, and
were especially pronounced in the northwestern Gulf. Furthermore, an Index of Reproductive
Importance showed that young fish have been contributing far less to the spawning
stock in recent years, while older fish, age eight and up, are contributing more,
when compared to fish from the same age groups sampled in the previous decade.

Coincident with these changes in reproductive output, fishing pressure has steadily
declined gulf-wide, and spawning stock biomass and spawning potential ratio have increased.
Thus, it is possible that the age structure of the red snapper stock is becoming less
truncated, or that reproductive efforts observed are due to the temporary influence
of recent strong year classes — fish born in the same year — produced in 2004 and
2006 as they begin to reach full reproductive potential. If the latter is true, careful
documentation of the stock’s reproductive dynamics during a time of population growth
provides new understanding at the meta-population spatial and decadal temporal scales.
In contrast, if the former is true, a truncated age structure due to overharvest can
limit the productivity of the Gulf red snapper stock. In addition, it was discovered
that red snapper females in the northwestern Gulf collected on natural reefs and banks
have much higher reproductive output than those on artificial reefs.

Their manuscript, “Temporal and Spatial Comparisons of the Reproductive Biology of
Northern Gulf of Mexico (USA) Red Snapper (Lutjanus campechanus) Collected a Decade
Apart,” has been approved for publication by The Public Library of Science ONE. To
their knowledge, this comparison is the first of its kind for red snapper in the Gulf
of Mexico. Their findings have implications for the management and long-term sustainability
of this species. The manuscript may be found online at http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0172360